It's hippo-hurray for Vic zoo mum Petre

If behind every great man is an even greater woman, who gets the credit for a healthy, happy hippo calf?

Melbourne zookeepers reckon pygmy hippo Obi has mum Petre to thank for his strong start in life.

Three-week-old Obi took his first swim in the zoo's big pool, with Petre nudging him along all the way.

Petre hasn't let Obi stray too far from her side, with zoo keepers impressed at how little they've had to help with her fourth calf.

"She's been getting better each time, and this one we haven't had to do anything, we haven't had to help her at all, so that's really nice," Melbourne Zoo's Wild Sea Manager, Justin Valentine, said after Obi's dip on Thursday.

Hippos are often born in the water, but building up their strength to swim isn't necessarily easy.

Obi has been having lessons in the Zoo's smaller pools, with his mum teaching him how to get in and out of the water.

While he's improving, Valentine says learning to swim can leave the little hippo a bit tired after only 10 or 15 minutes.

Even with his mum looking over his shoulder, Obi is expected to take a few tumbles as he settles into zoo life.

"There's still a few things - logs and things trip him up from time to time, but she's there to pick him up," Mr Valentine said.

At the moment the confident little calf tips the scales at 13.5 kilograms, but he may weigh as much 300 kilograms when he's fully grown.